In lock and locking mechanisms, there has been the use of one or of two keys relating to the lock to program or set the mechanism to one of two positions for a change in operating mode. For example, a lock may be constructed to receive a key for unlocking a device or machine so that operation thereof is permissible and the same lock may be constructed to receive a second key for a different operation which may be in the form of a checking nature or to reset the device or machine. Normally, the structure for changing or for interrupting a key operation requires complicated and complex mechanism and there is a susceptibility of interference between the operating mode and the check or reset mode which may cause errors in the operation. Additionally, it is desirable that setting of a lock mechanism be an initiation point for a further switching operation and this feature has been omitted in prior machines of the type described.
Such devices or machines may be designed to provide a plurality of functions with a single unit. For example, a cash register is operable to perform several functions as registration, correction of error registration, registration of article returned, checking, settling account, settling total account and the like. While the machine operator may be required to perform only one or two of these functions, the machine should be controlled so that it can be operated by other personnel for one or more preselected functions. When a cash register is used in a department store, the register need be controlled in a manner that it can be operated by sales persons for registration; by floor supervisors for registration, correction of registration, and registration of article returned; by accounting personnel for checking and various like functions; and by a manager for any or all of these operations.
In this respect, a conventional cash register may be provided with a function selector switch connected to a plurality of locks and each operator is permitted to use only one or more keys for his purposes. The use of only one or two keys is a disadvantage as it necessitates the provision of two or four separate locks for a single machine, or in the above-mentioned situation, four different operators of the machine utilize four different types of keys. The provision of more than two separate locks for a single machine would complicate the construction thereof and would not be preferred. Another disadvantage of a conventional lock is that it provides no mechanism for reliably preventing the key from being rotated inadvertently and wherein erroneous operations would occur.